In recent years digital image acquisition has become more and more popular. In particular, acquisition of digital color images has found widespread use in many technical fields. Digital color images are usually acquired by acquiring images for three primary colors and combining these images to a color image. Usually, the three primary colors red, green, and blue are used (RGB). However, other primary colors such as cyan, yellow, magenta (CYM) are in principle possible as well. Thus, an ideal system for acquisition of color images requires three monochrome photo-sensitive elements per pixel of the image, i.e. a monochrome photo-sensitive element each for red, green, and blue in case of an RGB image. Each pixel of such an image thus consists of three components corresponding to the proportions of the primary colors or base colors. Due to economic reasons, use of a single sensor provided with a color filter array (CFA) has become widely accepted on the market. Each photosensitive element of such a sensor is provided with a primary color filter for one of the three primary colors and thus will only detect one of the three primary colors.
The most commonly known color filter array is the so-called Bayer RGB color filter array as e.g. disclosed in U.S. Pat. No. 3,971,065. In this color filter array, 50 percent of the photosensitive image elements comprise a green filter (G), while 25 percent comprise a red filter (R) and the remaining 25 percent comprise a blue filter (B). As a consequence, the missing proportions of primary colors of a pixel have to be interpolated from the surrounding pixels. Due to this, the image quality becomes deteriorated as compared to an arrangement of three independent color sensors per pixel since the color resolution is reduced. Furthermore, depending on the chosen method for interpolation, several image artifacts can occur which may deteriorate the overall appearance of the acquired image.
There can be found complex high-quality algorithms, on the one hand, and simpler methods which can be implemented in hardware having low complexity but do not provide satisfactory quality, on the other hand.
US 2004/0179752 A1 discloses a method for interpolating a full color image from an array of single color sensors. According to this method, first all green pixels are reconstructed and, based on this reconstruction, the red and blue pixels are reconstructed. Thus, a frame memory for storing data corresponding to a full frame is required to hold the full image to be reconstructed and to complete the image step by step.